The invention relates to a filter insert of nonwoven material in the form of a pleated pack, and to a method for the manufacture thereof.
Such filter inserts, used especially as air filters for motor vehicles, usually consist of a filter material of paper or nonwoven material, for example, arranged in pleats.
In apparatus in which a measured air flow is required, as for example in automobile air conditioners, it is necessary to establish the number and width of the pleats according to their filtering characteristics, such that the pressure loss caused by the dust filter will be minimized.
In the manufacture, first the filter pack is shaped, and the hollow spaces formed by the pleating are cemented at the outer edges with a solid additional material. Then the distance between the individual pleats thus formed is adjusted, and then this pack is set in a frame.
By means of polyurethane soft foam systems, for example, the bottom edges of the pleated pack thus formed are bonded together, so that the spacing of the individual folds is fixed. This foam serves simultaneously as framing and as sealing means in order afterward to achieve a leakage-free sealing off of the filter inserted into a corresponding housing.
The filter inserts thus fabricated often do not have sufficient inherent stability, and require a correspondingly complex framing for their installation.
Another disadvantage consists in the recycling of the filter inserts. Additional materials, such as glues and frames, must also be disposed of.
In the known method of manufacture a plurality of working steps are necessary, such as cementing with additional materials, foaming, or also injection molding. It is also disadvantageous that the liquid sealing composition at the outer edges of the pleats expands and reacts in the mold, i.e., it also flows into the area behind the actual pleated pack and thus partially restricts the air inlet or outlet opening, so that the pack is not optimal as regards pressure loss.
Setting out from the above state of the art, it is the aim of the present invention to devise a filter insert which will not have the above-described disadvantages. At the same time the inherent stability of the insert is to be improved. Materials other than that of the filter material itself are to become largely unnecessary. The manufacturing process is to require fewer operations, and in particular it is to be possible to eliminate the liquid sealing composition at the outside edges.